Patent GB-1011456-A (GB)
Title: Poromeric material and method of making
IPC: D06N3/00
Filed: 1964-02-13
Abstract: A microporous layer of flexible polymeric material containing randomly dispersed staple fibres is made by dispersing the polymeric material and fibres in a liquid which is solvent for the polymeric material and non-solvent for the fibres and coagulating into a micro-porous structure by bathing with a liquid non-solvent for the polymer and miscible with the solvent, removing the solvent and then the non-solvent and drying.  The layer may be formed without the fibres.  The preferred polymer is a polyurethane elastomer possibly combined with a vinyl chloride polymer and a useful solvent is N,N-dimethyl formamide.  The polyurethane elastomer is prepared by reacting an organic diisocyanate with an active hydrogen containing polymer such as a polyalkylenether glycol or a hydroxyl terminated polyester to produce a prepolymer which is then reacted with a chain extending compound such as water.  The polymeric glycol may be replaced by a simple non-polymeric glycol (ethylene or propylene glycol). Examples of di-isocyanates and glycols are given.  In a particular example a solution of polyurethane elastomer is prepared by mixing polytetramethylene-ether glycol with tolylene-2-4-di-isocyanate, then adding methylene-bis-(4-phenylisocyanate) to yield a prepolymer with isocyanate end groups.  This is then dissolved in dimethylformamide and the resulting solution added to a solution consisting of a chain extender dissolved in dimethyl formamide; the chain extender is N-methyl-bis-amino-propylamine and hydrazine hydrate, to form a polyurethane solution.  A polymer solution is then prepared by mixing in suitable amounts the polyurethane solution and a solution of polyvinyl chloride in dimethyl formamide.  This is then converted to a colloidal dispersion by adding water and dimethyl formamide. Staple nylon fibres are then blended in with the dispersion which is coated on to a non-woven fabric and coagulated into a microporous structure by floating and sinking the coated material in cold water, then leaching in hot water to remove the dimethyl formamide, then dried and compacted in a press.ALSO:Poromeric sheet material comprises (A) a vapour-permeable non-woven fabric layer of entangled and interlocked fibres, and (B) a microporous layer of flexible polymeric material containing randomly dispersed staple fibres the majority of which are free of contact with one another.  The density of layer (B) is at least 0,4 gm. per c.c. and the ratio by weight of polymeric material to staple fibres is from 80:20 to 97:3.  The fabric for layer (A) is preferably in the form of a ligated fibrous mat of synthetic, crimped, organic fibres, shrunk from its original area and impregnated with a porous flexible polymeric material. Natural fibres may also be used.  The polymeric material for layer (B) is preferably a polyurethane elastomer or a blend thereof with a vinyl chloride polymer.  Also used are vinyl halide polymers polyarides, alkyl esters of acrylic and methacrylic acids, chlorosulphonated polyethylene and copolymers of butadiene and acrylonitrile.  Curatives, colouring agents, plasticizers, stabilizers and fillers may be blended with the polymeric material. The staple fibres are preferably nylon or polyethylene terephthalate but may be of rayon or acetate acrylic or polyester fibres.  To make layer (B) the polymeric material and staple fibres are dispersed in a liquid which is solvent for the polymeric material and non-solvent for the fibres.  The dispersion is coated or extruded on to layer (A) and coagulated into a microporous structure by bathing with a liquid non-solvent for the polymer and miscible with the solvent liquid removing the solvent and then removing the non-solvent and drying. The resulting coated non-woven fabric is compacted in a press to increase the density of the layer (B) to at least 0,4 gm. per c.c.  A useful solvent is N,-N-dimethyl formamide (others are referred to). The preferred polymeric component is a polyurethane elastomer prepared by reacting an organic diisocyanate with an active hydrogen containing polymeric material such as a polyalkylene-ether glycol or a hydroxyllaminated polyester to produce a prepolymer which is then reacted with a chain extending compound such as water.  Examples of diisocyanates and glycols used are given.  A third layer (C) of microporous vapour permeable flexible polymeric material may be applied to layer (B) formed in the same way as (B) but without the staple fibres.